Veering even further into the House Rules territory:
IMC we ruled that all Sorcerers could use a "Spells Known" slot to learn a metamagicked spell in place of a normal spell, assuming they had the appropriate MM feat. So, you get to 10th level, and instead of picking a new level 5 spell you take Empowered Fireball. It's still spell level 3 for DC purposes, and you can't turn off the Empower effect, but it now casts at the normal 1-action rate. (To pick this spell, you'd need to have Empower Spell already, but you don't need to already know Fireball)
Plain Sailing's "Sorcerous Mastery" Feat is better, of course, but this is an easy house rule to convince a DM to allow, and it doesn't cost you a Feat.
EDIT: Forgot to add, someone once suggested that if a Sorcerer takes the Spell Thematics Feat (picking one spell at each spell level), they should be able to metamagic those spells freely since they're his signature abilities.
You could probably build a whole big Feat tree using Spell Thematics, PS's Sorcerous Mastery, and the Signature Spell feat. Throw Eschew Materials in there and you've got a nice chain.